Genetic, viral and immunologic factors in a murine model of autoimmune disease and malignant lymphomas, the New Zealand Black (NZB) mice, will be analyzed. These factors will be studied in genetic crosses between NZB mice and various nonautoimmune strains that permit the segregation of virologic events from autoimmune manifestations. NZB mice, that have been rendered tolerant to DNA with consequent amelioration of autoimmune disease will also be analyzed for unlinking of viral expression from immunologic events. The mechanism of suppression of ecotropic murine leukemia viruses (MuLV) in NZB mice and their F1 hybrids will be investigated. The genetic determinants controlling xenotropic MuLV inheritance and expression will be analyzed.